The present invention relates generally to mobile sewer cleaning machines and, more particularly, to a method and apparatus for monitoring the length an elongated sewer cleaning tool is extended from such a machine.
A mobile sewer cleaning machine typically includes an elongated sewer cleaning tool wound on a reel that is mounted in a compartment of a truck body or trailer. A control panel for controlling the machine and the drive for the reel is typically mounted on the machine adjacent the reel. The tool may comprise a high pressure hose, a series of rods interconnected to define a required tool length, a spiral wound "snake", or other appropriate tool which includes an appropriate cleaning attachment secured to its end.
In such machines, a length of tool is unwound and paid out from the reel under the control of an operator standing at the control panel alongside the hose. For rods, snakes and the like, the cleaning attachment is forced through the sewer. For the high pressure hose, the cleaning attachment typically comprises a jet nozzle which pulls itself and the hose through the sewer by the force generated by a rearwardly directed high pressure water stream emanating from the nozzle while at the same time washing the debris in the sewer back toward the manhole entrance to the sewer. Whatever the tool, after the sewer has been cleaned or if a reverse cleaning pass is to be made, the reel drive is reversed to thereby retract the tool from the sewer and wind it back onto the reel.
Normally the length of sewer cleaning tool provided is somewhat longer than that necessary to clean the longest sections of sewer which extend between adjacent manhole entrances to the sewer. Thus, an operator will open a manhole, clean the section of sewer which extends from the opened manhole to the next adjacent manhole, retract the tool from the sewer and move the machine to the next adjacent manhole to continue the cleaning operations for the entire run of sewer to be cleaned. For such operation, the operator must keep track of the length of tool which has been extended from the machine and, knowing the distance to the next adjacent manhole, stop the machine after the section of sewer interconnecting the manholes has been cleaned.
To this end, mechanical counters have been coupled to the cleaning tool as shown for example is U.S. Pat. No. 4,540,017. While such mechanical counters provide an accurate indication of the length of cleaning tool extended from the machine to permit an operator to properly clean sewer sections between adjacent manholes, they require substantial attention on the part of the operator who must frequently monitor the mechanical counter to know when the section of sewer has been cleaned. Such monitoring is difficult under the least distracting conditions on manual cleaning machines which require substantially more operator attention and on automatic machines becomes almost impossible for all but the most attentive operators.
Accordingly, there is a need for a method and apparatus for monitoring sewer cleaning tool extension from a sewer cleaning machine which is not demanding on an operator of the machine and, preferably, warns the operator a short time before operator action is required such that it relieves the operator of tedious duties and is not dependent for its effectiveness upon frequent attentive monitoring by the operator. Such a tool extension monitoring method and apparatus would help ensure the most efficient operation of a sewer cleaning machine and also help prevent potential operating problems which might otherwise occur if the machine is permitted to operate beyond its proper operating limits.